- fix bug wrt posix_memalign(3) of blocks between half a page and a page

- document posix_memalign() does not play nice with reacallocarray(3) and
freezero(3)

src/lib/libc/stdlib/malloc.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: malloc.c,v 1.224 2017/04/22 09:12:49 otto Exp $	*/
+/*	$OpenBSD: malloc.c,v 1.225 2017/05/13 07:11:29 otto Exp $	*/
 /*
  * Copyright (c) 2008, 2010, 2011, 2016 Otto Moerbeek <otto@drijf.net>
  * Copyright (c) 2012 Matthew Dempsky <matthew@openbsd.org>
@@ -1974,15 +1974,20 @@ mapalign(struct dir_info *d, size_t alignment, size_t sz, int zero_fill)
 }
 
 static void *
-omemalign(struct dir_info *pool, size_t alignment, size_t sz, int zero_fill, void *f)
+omemalign(struct dir_info *pool, size_t alignment, size_t sz, int zero_fill,
+    void *f)
 {
 	size_t psz;
 	void *p;
 
+	/* If between half a page and a page, avoid MALLOC_MOVE. */
+	if (sz > MALLOC_MAXCHUNK && sz < MALLOC_PAGESIZE)
+		sz = MALLOC_PAGESIZE;
 	if (alignment <= MALLOC_PAGESIZE) {
 		/*
-		 * max(size, alignment) is enough to assure the requested alignment,
-		 * since the allocator always allocates power-of-two blocks.
+		 * max(size, alignment) is enough to assure the requested
+		 * alignment, since the allocator always allocates
+		 * power-of-two blocks.
 		 */
 		if (sz < alignment)
 			sz = alignment;

src/lib/libc/stdlib/posix_memalign.3

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: posix_memalign.3,v 1.3 2012/06/18 17:03:52 matthew Exp $
+.\"	$OpenBSD: posix_memalign.3,v 1.4 2017/05/13 07:11:29 otto Exp $
 .\" Copyright (C) 2006 Jason Evans <jasone@FreeBSD.org>.
 .\" All rights reserved.
 .\"
@@ -28,7 +28,7 @@
 .\"
 .\" $FreeBSD: src/lib/libc/stdlib/posix_memalign.3,v 1.3 2007/03/28 04:32:51 jasone Exp $
 .\"
-.Dd $Mdocdate: June 18 2012 $
+.Dd $Mdocdate: May 13 2017 $
 .Dt POSIX_MEMALIGN 3
 .Os
 .Sh NAME
@@ -56,9 +56,14 @@ must be a power of 2 at least as large as
 Memory that is allocated via
 .Fn posix_memalign
 can be used as an argument in subsequent calls to
-.Xr realloc 3
+.Xr realloc 3 ,
+.Xr reallocarray 3
+and
+.Xr free 3 ,
+but not
+.Xr recallocarray 3
 and
-.Xr free 3 .
+.Xr freezero 3 .
 .Sh RETURN VALUES
 The
 .Fn posix_memalign